Microstructural and morphological aspects of plutonium hydride A thesis submitted to the University of Manchester for the degree of Nuclear EngD in the Faculty of Engineering and Physical Sciences 2015 Martin Brierley School of Materials Contents Contents .......................................................................................................... 2 Table of figures .............................................................................................. 10 Word count .................................................................................................... 16 Glossary ........................................................................................................ 17 Abstract ......................................................................................................... 18 About the Author ............................................................................................ 19 Declaration .................................................................................................... 19 Copyright statement ...................................................................................... 20 Personal Statement ....................................................................................... 21 Acknowledgements ....................................................................................... 22 Chapter 1 Introduction ................................................................................. 23 1.1 Aims of the research ....................................................................... 24 1.2 Introduction to plutonium ................................................................. 25 1.2.1 Origins of plutonium ................................................................... 25 1.2.2 Isotopes and radioactivity .......................................................... 26 1.2.3 Fission ....................................................................................... 27 1.2.4 Allotropes of plutonium .............................................................. 28 1.2.4.1 Alpha plutonium ................................................................................ 29 1.2.4.2 Delta plutonium ................................................................................. 30 1.2.5 Transition between phases ........................................................ 32 1.2.6 Chemical reactivity ..................................................................... 33 1.2.7 Uses of plutonium ...................................................................... 35 1.2.8 Why is the corrosion of plutonium important? ............................ 35 1.2.9 Health ........................................................................................ 36 1.2.10 Pyrophoricity .............................................................................. 38 1.2.11 Environment ............................................................................... 39 1.3 Introduction to plutonium oxide ....................................................... 40 1.3.1 Rate of reaction with plutonium metal ........................................ 43 1.3.2 Stability ...................................................................................... 43 1.4 Plutonium hydride ........................................................................... 44 1.4.1 Rate of reaction with plutonium metal ........................................ 48 1.4.2 Stability of the hydride phases ................................................... 49 1.4.3 Sources of hydrogen .................................................................. 49 Chapter 2 Literature review ......................................................................... 50 2.1 Historical research into plutonium hydride ....................................... 51 2.1.1 Initial studies .............................................................................. 51 2.1.2 Solid solubility of hydrogen in plutonium and plutonium hydride 52 2.1.3 Hydriding kinetics ....................................................................... 52 2.1.4 Activation energy ....................................................................... 53 2.1.5 Pyrophoricity .............................................................................. 53 2.1.6 Hydride growth behaviour .......................................................... 54 2.1.7 Hydride nucleation ..................................................................... 55 2.1.8 Continued growth ....................................................................... 56 2.2 Hydriding work undertaken on other metal-hydride systems ........... 56 2.2.1 5f elements (actinides) ............................................................... 57 2.2.1.1 Uranium ............................................................................................. 57 2.2.2 4f elements (lanthanides)........................................................... 60 2.2.2.1 Cerium ............................................................................................... 60 2.2.2.2 Gadolinium ........................................................................................ 60 2.2.2.3 Holmium............................................................................................ 61 2.2.3 Transition metals ....................................................................... 61 2.2.3.1 Zirconium and zirconium alloys ....................................................... 61 2.2.3.2 Titanium ............................................................................................ 62 2.3 Models of the hydriding process ...................................................... 63 2.3.1 Nucleation models ..................................................................... 63 2.3.2 Growth models ........................................................................... 65 2.3.3 General models ......................................................................... 66 2.3.4 Comparison of models ............................................................... 67 Chapter 3 Experimental ............................................................................... 68 3.1 Background ..................................................................................... 69 3.2 Cerium experiments ........................................................................ 69 3.2.1 Material details ........................................................................... 69 3.2.2 Pre-hydriding sample preparation .............................................. 70 3.2.2.1 Sawing ............................................................................................... 70 3.2.2.2 Cleaning ............................................................................................ 71 3.2.2.3 Surface preparation ........................................................................... 71 3.2.3 Exposure to hydrogen ................................................................ 71 3.2.3.1 Gas handling rig ................................................................................ 71 3.2.3.2 Reaction cell ...................................................................................... 72 3.2.3.3 The hydriding reaction ...................................................................... 72 3.2.4 Post hydriding sample preparation ............................................ 73 3.2.5 Light microscopy ........................................................................ 74 3.2.6 Secondary Ion Mass Spectrometry ............................................ 74 3.2.7 Scanning Electron Microscopy ................................................... 76 3.2.7.1 Secondary Electron Imaging ............................................................. 77 3.2.7.2 Backscattered Electron Imaging........................................................ 78 3.2.7.3 Energy Dispersive Spectroscopy ....................................................... 78 3.2.8 Sample coating .......................................................................... 79 3.2.9 Ion milling ................................................................................... 79 3.2.10 Vickers hardness ....................................................................... 80 3.2.11 Nanoindentation ......................................................................... 81 3.2.12 Atomic Force Microscopy........................................................... 86 3.3 Plutonium experiments .................................................................... 88 3.3.1 Preparation for hydriding reaction .............................................. 88 3.3.2 Surface analysis preparation ..................................................... 90 3.3.3 Cross sectional analysis preparation ......................................... 90 3.3.4 Sample coating .......................................................................... 91 3.3.5 Ex-situ hydriding ........................................................................ 91 3.3.6 Scanning electron microscopy for plutonium ............................. 92 3.3.6.1 Analysis modes ................................................................................. 94 3.3.6.2 Sample transfer to the FEGSEM ....................................................... 95 3.3.6.3 Ion milling ......................................................................................... 95 3.3.6.4 In-situ hydriding ...............................................................................